1. Field of the Invention
The present invention relates generally to an apparatus and method for preventing data transmission delay, and in particular, to an apparatus and method for preventing data transmission delay using a combining technique in a high-speed router and a switch.
2. Description of the Related Art
With the rapid increase in the number of Internet users, extensive research is being conducted to determine new methods of increasing the data rate. As a result of the research, various techniques for saving transmission resources and increasing throughput by reducing the overhead of transmission data are being recently proposed. The typical techniques include an overhead compression technique and a packet data combining technique.
A protocol such as TCP/IP (Transmission Control Protocol/Internet Protocol) is generally used when transmitting packet data. The protocol adds a header of 40 30 bytes or more to transmission data A transmission overhead of a predetermined amount occurs regardless of an amount of the actual transmission data. This process deteriorates system performance.
The overhead compression technique compresses headers by 4 to 6 bytes, and adds the compressed headers to the transmission data. This technique can reduce the total number of transmissions, thereby contributing to an increase in transmission throughput and a decrease in a round trip time.
The packet data combining technique combines two or more data packets and then transmits the combined data in one overhead packet in order to reduce the overall overhead of each layer. This also decreases a time delay occurring due to a protocol characteristic in which a header and a tail are added to each transmission data. Such an overhead is larger in size in a wireless environment than in a wired environment. The combining technique performs better in a medium access control (MAC) protocol, and is generally used when transmitting data in a high-speed router or a switch.
FIG. 1 is a block diagram illustrating a structure of a conventional transmission module for preventing transmission delay of packet data. Referring to FIG. 1, the data transmission module is comprised of a transmission manager 10 for controlling management of transmission data and preprocessing for the protocol header, and a transmission protocol engine 20 for transmitting actual packet data according to a transmission protocol.
The transmission manager 10 includes a transmission queue 11 for storing data and a frame processor 12 for combining data packets stored in the transmission queue 11, for data management. Further, the transmission manager 10 includes a transmission wait timer (Tx_Wait_Timer) for delaying packet data stored in the transmission queue 11 in order to combine the packet data with subsequent packet data received.
The transmission protocol engine 20 includes a transmission buffer 21 for storing packet data received from the transmission queue 11 to transmit the stored packet data at a transmission time, and a transmission controller 22 for controlling transmission of the packet data. The operation of combining transmission packet data in the transmission module stated above will now be described with reference to FIGS. 2A and 2B.
As illustrated in FIG. 2A, if new packet data is received in an idle state, the frame processor 12 delays the received packet data by driving the transmission wait timer. As illustrated in FIG. 2B, if previous packet data is stored in the transmission queue 11 in a busy state of a channel, the frame processor 12 combines the currently received packet data with the previous packet data, and transmits the combined packet data to the transmission buffer 21. The transmission buffer 21 then stores the combined packet data and transmits the stored combined packet data to a corresponding destination at a transmission time.
When a data reception rate is low, there is low probability that two or more data packets will accumulate in the transmission queue 11. In this case, data received at the transmission queue 11 is not immediately sent to the transmission buffer 21, but is delayed using the transmission wait timer, which in turn increases the probability that data will accumulate in the transmission queue 11. In the combining technique, even though data can be rapidly transmitted without transmission delay in view of a good channel condition, transmission data is delayed due to the transmission wait timer.
In addition, although data combined by the transmission buffer 21 is stored, if the stored combined data cannot be transmitted because of a busy state of a channel, data will accumulate in the transmission queue 11. In order to increase transmission throughput, it is effective to combine data in the transmission buffer 21 with data in the transmission queue 11. However, the conventional combining technique can combine only the data in the transmission queue 11, since the transmission manager 10 cannot consider a situation of the transmission buffer 21.